Light and utility poles have long been made of traditional materials such as wood, steel, cast iron, aluminum, and concrete. Each of these materials suffers from one or more disadvantages. For example, these traditional materials are heavy, expensive, electrically conductive, unattractive, and prone to corrosion. Light and utility poles made from electrically conductive materials are potential electric shock hazards. In addition, light and utility poles made from these traditional materials are difficult and expensive to install.
Period style poles serve the same function as the traditional poles, however, the period style poles are more decorative. A majority of factories and foundries that manufactured period style poles are no longer in existence. The tooling and original patterns have long been lost and many of the facilities closed due to environmental problems.
Recently, composite poles made from fiberglass and resin (polyester or epoxy) have become a widely accepted alternative to the traditional and period style poles. These composite materials are corrosion resistant, lightweight, inexpensive, attractive, and non-conductive. Further, light and utility poles made from composites can be directly buried into the ground because the composite material will not corrode or rot. These composite poles are typically made by a number of conventional processes such as filament winding, centrifugal casting, pultrusion, and resin transfer molding. The poles may be straight or tapered, and may have various outside surfaces such as flutes, textures, or smooth contours.
These methods of manufacturing composite poles are selected to provide the poles with certain desired characteristics. For example, the appearance of the outside surface is important, and great expenses are taken to achieve a high quality surface. In addition, the strength of the pole is important, as it must carry light fixtures, signs, traffic signals, and the like in high wind situations. A method that increases the strength and improves the decorative appearance of the pole without adding excess cost is thus commercially important.
One such method of producing a pole includes making a fiberglass pole by conventional means such as filament winding or centrifugal casting. In this method, a decorative mold such as a tapered fluted or octagonal shape is prepared by applying a gel coat of polyester resin to the inside of the mold. After the gel coat partially polymerizes, a polyester fiberglass skin is applied to the gel coat. The polyester fiberglass skin can be applied by hand lay-up means or through the use of a fiberglass chopper gun, which applies resin and chopped fiberglass together. In either of these processes, the fiberglass skin must be hand rolled out to compact the fiberglass and force it to conform to the mold detail. Compacting the fiberglass is labor intensive and expensive. After the fiberglass skin polymerizes, the fiberglass pole is centered in two mold halves, which are joined together and placed in an upright position. A mix of polymer concrete (polyester resin and aggregate) is then poured into the annular space between the fiberglass skin and the inside fiberglass pole. After polymerization is complete, the mold is opened and the completed pole removed. The completed pole is more rigid and stronger than the fiberglass “core pole,” and has a decorative outside appearance such as a fluted or octagonal surface.
Another method of producing a decorative fluted pole includes placing layers of fiberglass cloth into a mold which may be gel coated as in the previous example. A mandrel such as a metal pole is treated with a mold release and inserted into the mold. Polyester resin is then forced into the space between the mandrel and the mold by either pressure, vacuum, or a combination of both, and allowed to polymerize. The mandrel is then withdrawn, and the pole removed from the mold. Because there is no fiberglass “core pole” with this method, these poles can be manufactured for a lower cost compared to the poles made by the first method described above, however, these poles are typically limited to lower stress situations.
A third method of producing a decorative composite pole includes loading fiberglass reinforcement (typically in a woven or knit form) into a metal tube, introducing polyester resin into the tube, and rapidly spinning the metal mold tube. This centrifugal force typically forces the fiberglass reinforcement into the flutes, however, it also tends to bridge between the flutes and cause weak areas in the pole. After polymerization is completed, the pole is withdrawn from the mold tube. In addition to the mentioned bridging, the excess resin goes to the inside of the pole, since it has a lower specific gravity than does the fiberglass. This unreinforced resin is brittle, and adds little to the strength of the pole. As can be appreciated to one skilled in the art, it becomes more difficult to manufacture a pole using this method when the pole is both tapered and fluted as opposed to manufacturing a pole that is round and straight.
The fourth method of producing a decorative composite pole consists of preparing a two-piece split decorative mold with a mold release and gel coat. Fiberglass mat wet out with polyester resin is applied to one mold half with excess laminate on the other side of the mold. A rubber bag or hose is placed on the wet laminate, the excess laminate folded over the bag, and the second mold half is installed and clamped into place. The bag is then inflated, forcing the wet laminate against the mold surface until the resin cures. The manufacturing process results in variable quality and relatively high costs.
In addition to new installations, there are huge numbers of existing poles installed which are corroding or could benefit from a more decorative appearance, but the cost of replacing them is extremely high, especially in urban locations. A method of retrofitting and protecting these existing poles in place would also be desirable and commercially important.